The present invention relates generally to devices for injecting two or more medications simultaneously and, more particularly, to a medication injection device having improved dose setting and injection capabilities.
It is medically desirable in the treatment of certain conditions of the human body to administer two or more types of medication simultaneously. The treatment of diabetes is one such example. Under certain conditions, it is desirable to simultaneously deliver two types of insulin: fast acting insulin and an intermediate acting insulin, such as isophene insulin, which takes effect more slowly but for a longer period of time. Also, a longer acting type of insulin called ultralente is available. In order to most accurately simulate the natural glucose curve of the body, the insulin user injects different ratios or combinations of these insulins several times daily.
In order to achieve such injection capability, there have been developed injection devices in which separate cartridges of a desired medication are housed. It is desirable that both medications be delivered to a patient through a single needle instead of two or more needles. Therefore, such injection devices have a manifold assembly that enables the medications to be mixed together prior to injection.
One such type of injection device is proposed in U.S. Pat. No. 5,253,785. This patent asserts a dispenser for injecting variable mixed proportions of NPH and regular human insulin. The dosages of each medication are set prior to delivery. Dosing is achieved by rotating a dose knob to translate a dosage adjuster to a retracted position. The second dosage knob is adjusted in a similar manner. The dosage adjusters are coupled to a sliding body. After the appropriate dosages are set, the sliding body is forced forwardly, which causes the drive stems to translate forwardly. Since the drive stems are connected to pistons within each medication cartridge, movement of the drive stems drives the pistons forward to expel liquid from the cartridges. The forward stroke of the sliding body is limited by the distance set by the dosage adjusters.
Another type of dual medication injection device is proposed in PCT International Application No. PCT/US93/11044. In this device, dosage knobs are rotated to translate the dosage adjusters to their retracted positions. Movement of the dosage adjusters compresses springs, which engage flanges on the adjusters. This compression preloads the drive stems so that moving the needle assembly from the predelivery position to the delivery position causes the dosages of pharmaceutical to be automatically driven from the pharmaceutical chambers, past the check valves and through the doubled ended needle cannula.